Method and apparatus for heattreating loose bulk materials



w. A. REANEY METHOD ANDv APPARATUS FOR HEAT TREATING LOOSE BULK4MATERIALS Filed June 27, 1945 @Swim l .S u weil koi .$3.50

I Il W Qu koks@ Patented Oct. 29, 1946 METHOD AND'APPARATUS FOR HEAT-TREATING LOOSE BULK MATERIALS Watford A. Reaney, Delaware, Ohio--Applcation June 27, 1945, Serial No. 601,763

vs' cnims. (ci. 263-22) This invention relates to an improved processand apparatus adapted particularly for effecting the calcination ofcalcareous materials, such as limestone, marl or the like, a generalobject of the invention being to-provide a new and improved process andapparatus by which such calcination may be carried out with greaterthermal efciency .than heretofore has been obtainable.

. In the production of lime from limestone. it is'the ordinary practiceto pass limestone through arotary kiln. While inthe kiln, the'limestoneis iired to temperatures in the order of 1400. to 2000 degrees F. Suchburning of the limestone liberates its-carbon dioxide content, leavingcalcium oxide or lime as the calcined product. The heated lime upon itsdischarge from the kiln is cooled and thereafter crushed to a requireddegree of iineness suitable for various uses. In this customaryoperation, the heat contained in the calcinedv lime is lostvto theatmosphere and is notV applied to any useful purpose. v

gAccordingly, it is another object of the invention to utilize moreefciently the available heat in hot calcined lime by bringing thelatter, immediately uponY its discharge, from a calcining kiln intodirect and intimate contact with'an unheated body of limestone beingcharged to a calcining operation so that the charging material willbepreheated by contact withthe hot lime A before being introduced intothecalcining kiln. y It is still another object of the present inventionto provide a lime-calcining system in which two or more rotary kilns arearrangedmin adjacent order with the positions of theirmaterial-receiving and discharging ends y reversed with respect to eachother, so thatthe hot lime discharged from one of said kilns may beconveniently brought into direct contact with cold limestone being fedas a charging* material to the inlet end of the other Of, said kilns. ni A further object is to provide a system of this character in uwhichcrushed limestone ofi-lne mesh is employed as a charging material forone of the duplex kilns and a coarser lime fed as the charging materialto the other kiln whereby, through a screening operation, to provide forthe separation of nished lime from the kiln-charging limestone followingheat-exchanging admixture thereol.; v

Still, a `further object of the invention is to provide a lime-calciningsystem in 'which' ad-y ditional-heat economies are obtained bydisposmeiner-adjacent i: the Combustioaeas. Outlet. of the kiln a heatexchanging meansgfor. p re-` 2 heating air employed in sustaining fuelcom bustion within the kilns.

The present invention constitutes a continuation-in-part of thedisclosures set forth in my priorapplication, Serial No. 491,962, ledJune 23,1943.

A further understanding of the invention will be obtained by referenceto the following description and the accompanying drawing.

In said drawing: Fig. l illustrates in schematic form a typica systemfor carrying out the invention; f

Fig. 2 is a detail view showing a slightly modified form ofheat-exchanging pit. Y

gThe apparatus disclosed in the accompanying drawing comprises a pair ofkilns, indicated at I and 2, said kilns bein-g preferably of the rotarydrum type. The drum of leach kiln is mounted as usual, with itslongitudinal axis slightly angular to the horizontal, each drum beingsupported and rotated by conventional means. The upper ormaterial-receiving end of each of the kiln drums enters a vertical flueorwaste gas outlety stack, shown at 6, the lower portion of each stackbeing provided with a limestone receiving chute 1. Partially crushedlimestone, for example, of such particle size that it will pass througha 21/2 inch to 11A; inch mesh screen, is delivered to the chute I of thekiln Iv in a manner hereinafter dei-ined. while crushed limestone offiner particle sizesuch as that which would pass through ascreen of 1inch to 1/'2 inch mesh is delivered to the inlet chute 'I of the kiln 2.The hot lime discharging end of each kiln is provided with a `fuelburner 8 and the fan or blower 9 of each of these burners has its airinlet side connected with a duct system I6. A portion of this system,forming a heat exchanger Illa, is disposed in each of the stacks 6, sothatI the air r'employed forv fuel combustion purposes in the kilns willbe preheated by the waste gases for more eilicient utilization inthekilns.r

AThe outlet end of each kiln is formed With a lime-discharging chute II,the latter being arranged over a pair of mixing pits shown at I2 and I3in order that the hot lime discharged from said kilns may be directlyreceived Within saidpits. The hot lime of coarser particle -sizedischarged from the kiln 2 is received in the pit I3, andis therebrought into heat exchanging contact or relationship with crushed coldlimestone of ner particle size. By this operation, the temperature ofthe limestone is raised to preheat the ne limestone before it isintroduced iiiioiheiraletchgte orthgkiln I After such heat exchange hastaken place, the coarse lime is separated from the smaller sizedparticles of preheated limestone. Advantageously, this may beaccomplished by providing the pit I3 with a conveyor type elevator I4,the upper or discharge end I5 of this elevator being disposed inregistration with an inclined screen I6, so that as the mixture ofcoarse lime and ne limestone passes over the screen, the ine preheatedlimestone will pass through the meshes of the screen for delivery to theinlet chute of the kiln I. The coarser lime gravitates to the lower endof the screen and from that point is conducted in any suitable mannertoaposition of storage.

A corresponding arrangement is provided for introducing the coarselimestone into the kiln 2. Coarse limestone in an unheated state and ata controlled rate of ilow is dropped into the pit I2 from a valved spoutI1, where the coarse limestone comes into intimate heat exchangingrelationship with the hot lime of iine particle size dischargedfrom thelime outlet II` of 'the kiln I. As this-mixture of lime and limestone cf4dii?- ferent particle size gravitates to the bottom of the pit I2, thesame is engaged by the conveyor elevatorv I9 andliftedithereby fordeposit on an inclined screen 2S. The mesh of this screen is such thatas the mixture passes thereover, the calcined lime of fine particle sizewill pass through the screen for delivery to storage as a finishedproduct, while the preheated coarse limestone will be discharged fromthe lower end of the screen 2Q into the inlet chuteof the kiln 2.

Thus, by utilizing the dual kilns, each handling limestone of determinedparticle size and differing from that handled by the other, I am enabledto obtain thermal eiciencies and economies substantially in excess ofsystems now in general uselfor the purpose set'forth.

Thus the hot lime, while it possesses its highest temperature, andimmediately upon its discharge from the kilns, is brought into intimateadmixture with the charging limestone, usefully absorbingthe heat of thelime and minimizing heat losses in a system of this kind. Anotheradvantage accruing from the dual and reversely disposed kilns is thefact that combustion air, used in sustaining fuel combustion, may beeffectively preheated in the gas outlet stack of each kiln and by ashort transfer line delivered to the-fuel burner of each adjacent kiln.If the dual kilns were not used, the transfer line for the preheated airwould necessarily extend the full length Vof a single kiln, and heatlosses therefore would be such as to render the air-preheating elementineiiicient.

As shown in Fig. 2, the bottom of the heatexchanging pits, in which abed of heat-exchanging lime and limestone is maintained, may befunnel-shaped to maintain intimate engagement between the hot lime andlimestone, and the restricted outlet 2i of the pit may be arrangedimmediately over the table of a vibratory feeder 23, by which the heatedmaterials maybe fed'by a controlled feed to the elevator.

In summary, it will be evident that the present invention provides asystem or mechanical process whereby hot burned lime, discharged fromeach of two rotary kilns placed in adjacent order with theirmaterial-receiving and discharging ends reversed, acts as a preheatingmedium for the cool limestone charged to each opposite kiln, and wherebythe ue kor-stack gases of each ofthe two kilns serves to preheat thefuel and intake combustion air of each opposite kiln.

I claim:

1. Process for heat-treating materials, which comprises advancing astream of materials of relatively coarse particle size through aconiined heating zone, simultaneously therewith advancing a secondstream of materials of relatively iiner particle size through a separateheating zone, bringing the heated materials discharged from each of saidzones into direct heat-exchanging and preheating relationship withpreviously unheated materials of a particle size diiering from that rofboth said streams of materials destined for delivery to each of theother zones, and separating the preheated materials from the finallyheated materials prior to the introduction of the preheated materialsinto their respective heating zones.

2. Process for heating dry bulk materials differing in particle sizewhich comprises advancing a stream of materials of relatively coarseparticle size through a conned heating zone, simultaneously therewithadvancing a `second stream of such materials possessing a iiner particlesize through a separate heating zone, bringing the heated materialsdischarged from said'zones finto direct heat-exchanging andpreheatingrelationship with the unheated materials undergoing chargingadvancement to said zones, and screening the preheated zone-chargingvmaterials from the finally heated'materi'als prior to the introductionof said charging materials into their respective heating zones.

3. Process for heat treating loose bulk granular materials dii'ering inparticle size which comprises advancing a stream of 'such materialscomposed of 'relatively large or coarse particles through a heatingkiln, simultaneously therewith advancing a second stream of suchmaterials possessing relatively smaller and finer particle size througha second heating kiln, bringing the nally heated materials dischargedfrom each ci said kilns into directheat exchanging relationship with thepreviously unheated charging materials undergoing delivery to each ofsaid kilns, and following such commingling of the heated and unheatedmaterials, separating the charging materials from the finally heatedmaterials and delivering the preheated charging materials to theirrespective kilns.

4. Process for burning limestone, comprising placing limestone ofrelatively coarse particle sizethrough a kiln which is maintained atsuch temperatures as to effect calcination of the limestone,simultaneously therewith passing limestone of relatively fine particlesize through a second kiln maintained at calcination temperatures,admixing the hot calcined lime of coarse' particle `size immediatelyupon itsv discharge from said rst kiln with quantities of unheatedlimestone of ne particle size and which servesas the charging materialfor the second-named kiln, subjecting said admixture to a screeningoperation to remove in'a separated state the preheated limestone of neparticle size, delivering such preheated fine limestone to the inletofthe second-named kiln, admixing with the hot calcined lime of iineparticle size discharged from said second kiln with bodies of unheatedlimestone of coarse particle size, screening said last-named admixtureto remove the calcined lime of fine particle size therefrom, anddelivering the preheated coarse limestone to the inlet offsaid'rstnamedkiln.A l l 5. Process for heat-treating loose bulk materials, whichcomprises advancing a stream of such materials composed of particlesrelatively coarse in size through a confined heating zone,simultaneously therewith advancing a second stream of such materialscomposed of particles of finer size through a separate heating zone,admixing with the hot coarse materials immediately upon their dischargefrom the firstnamed heating zone quantities of unheated ma terial offine particle size, the latter constituting the charging material forthe second heating zone, following heat exchange between said ad" mixedmaterials screening the same to separate the heat treated materials ofcoarse particle size from the preheated liner materials and deliver--ing the latter to said second-named heating zone, admixing with hotmaterials of lne particle size immediately upon their discharge from thesaid second-named heating zone quantities of un heated coarse materialto preheat the latter ma terial, prior to its delivery to the inlet sideof the first-named heating zone, and screening said last` namedadmixture to remove therefrom the heatedr material of fine particle sizeand delivering the preheated material of coarse particle size to thefirst-named heating zone.

6. A process of heat treating materials as dened in claim 5 and whereinthe material streams advancing through the separate heating zones movelongitudinally in opposite directions with respect to each other.

7. A process whereby hot burned lime dis charged from each of two rotarykilns placed in juxtaposition with their receiving and discharge endsreversed, acts as a preheating medium for the charging limestone of eachopposite kiln, and whereby simultaneously the llue gases of each of thetwo kilns so placed acts as the preheating element for the fuel andintake combustion air of each opposite kiln.

8. In combination, a pair of juxtaposed, cylin-v drical kilns disposedwith the material receiving end of one kiln adjacent the materialdischarging end of the other, a fuel burner of the blast type at thematerial discharging end of each kiln, a stack at the material receivingend of each kiln, and an air conduit in heat exchange relation with thegases passing through the stack of each kiln, said conduit deliveringair directly to the burner of the other kiln, whereby such air ispreheated, and travels over a relatively short path.

WARFORD A. REANEY.

